Large Ripple Research Articles

Direct active and reactive power control of 3-level NPC-fed DFIG considering power ripple minimisation

Despite the advantages of three-level neutral point clamp (NPC) converters compared with standard voltage source inverters (VSIs), most of the direct power control (DPC) strategies for doubly fed induction generator (DFIG) reported in the literature, only utilise VSIs. As regards three-level NPC converter generates higher number of voltage vectors compared with standard VSIs, This paper presents a DPC strategy for DFIG using three-level NPC converters in which three-level NPC voltage vectors are employed to reduce large power ripples of conventional DPC. Therefore, a new optimised switching table is derived. Using this table, DFIG provides not only elaborate active and reactive powers which track their reference values very well, but also large power ripple is compensated. Also, because of ripple reduction, total harmonic distortion of rotor current, stator current, stator voltage and grid line-to-line voltage is reduced in proposed strategy compared with conventional DPC. Simulation results show the effectiveness of proposed method and have a reasonable correspondence with theoretical and mathematical analysis.

The stratigraphic imprint of a mid-Telychian (Llandovery, Early Silurian) glaciation on far-field shallow-water carbonates, Anticosti Island, Eastern Canada; pp. 207–213

The near-field stratigraphic record of the Early Silurian glaciations is well documented in the literature. Data from far- field areas are, however, sparse. One of the best far-field stratigraphic records of these Llandovery glaciations is exposed on Anticosti Island in eastern Canada. Eight shallow-water paleotropical facies are present close to the mid-Telychian Jupiter- Chicotte formational boundary along the south-central coast of Anticosti Island. These can be grouped into three facies associations that include, from bottom to top: a carbonate facies association (FA-1), a mixed siliciclastic and carbonate facies association (FA-2) and an encrinitic facies association (FA-3). These mid- to outer-ramp strata represent deposition mostly from episodic, high-energy storm events as evidenced by their sharp bases, hummocky cross-stratification, large wave ripples, gutter casts and wave-enhanced sediment gravity flow deposits. Superimposed on a long-term regressive trend, one main transgressive- regressive (TR) sequence and four meter-scale TR cycles are evident, indicating a multi-order stratigraphic framework developed under the influence of glacio-eustasy. The Jupiter-Chicotte formational boundary, a regional discontinuity surface caused by a forced regression, corresponds to the onset of a far-field mid-Telychian glaciation.

Pulse-Train-Controlled CCM Buck Converter With Small ESR Output-Capacitor

The pulse-train (PT) control technique for switching dc-dc converters is simple to design and benefits from excellent control performance. Up to now, almost all of the works on PT control are focused on switching dc-dc converters operating in discontinuous conduction mode, with few works reported on PT control of switching dc-dc converters operating in continuous conduction mode (CCM). In this paper, a PT-controlled CCM buck converter is studied and a unique low-frequency oscillation phenomenon is revealed, which results in large undesired inductor-current and output-voltage variations. The effect of equivalent series resistance (ESR) output-capacitor on the low-frequency oscillation is examined. The results indicate that such oscillation occurs when the ESR output-capacitor is relatively small and disappears when it is relatively large. However, a larger ESR will result in a large output-voltage ripple. In order to avoid the low-frequency oscillation and, at the same time, to ensure a small output-voltage ripple, the ICRIF circuit is applied. In this way, a small ESR output-capacitor can be used to decrease the output-voltage ripple. Simulation and experimental results are provided to verify the theoretical analysis.

Novel Switching Table for Direct Torque Controlled Permanent Magnet Synchronous Motors to Reduce Torque Ripple

The Direct Torque Control (DTC) technique for Permanent Magnet Synchronous Motors (PMSM) is receiving increased attention due to its simplicity and robust dynamic response when compared with other control techniques. The classical switching table based DTC results in large flux and torque ripples in the motors. Several studies have been reported in the literature on classical DTC. However, there are only limited studies that actually discuss or evaluate the classical DTC. This paper proposes, novel switching table / DTC methods for PMSMs to reduce torque ripples. In this paper, two DTC schemes are proposed. The six sector and twelve sector methodology is considered in DTC scheme I and DTC scheme II, respectively. In both DTC schemes a simple modification is made to the classical DTC structure. The two level inverter available in the classical DTC is eliminated by replacing it with a three level Neutral Point Clamped (NPC) inverter. To further improve the performance of the proposed DTC scheme I, the available 27 voltage vectors are allowed to form different groups of voltage vectors such as Large - Zero (LZ), Medium - Zero (MZ) and Small - Zero (SZ), where as in DTC scheme II, all of the voltage vectors are considered to form a switching table. Based on these groups, a novel switching table is proposed. The proposed DTC schemes are comparatively investigated with the classical DTC and existing literatures through theory analysis and computer simulations. The superiority of the proposed DTC method is also confirmed by experimental results. It can be observed that the proposed techniques can significantly reduces the torque ripples and improves the quality of current waveform when compared with traditional and existing methods.

Precise Braking Torque Control for Attitude Control Flywheel With Small Inductance Brushless DC Motor

In this paper, a newly designed braking torque control scheme with improved toque estimation and control characteristics in a small inductance brushless DC motor is presented. The motor torque is estimated according to the back electromotive force (EMF) shape function that is fitted by neural network and corrected by temperature. Upon this, a hybrid braking torque control structure that combines dynamic braking and plug braking is proposed for the smooth and continuous braking torque. These two braking modes operate, respectively, in the relatively high- and low-speed ranges. During dynamic braking, a predictive torque control method is proposed to suppress the torque fluctuation that is induced by the supplying voltage namely back EMF descent. During plug braking, an effective torque ripple reduction method is designed to weaken the large torque ripple which is caused by high winding voltage, low winding impedance, and three-phase inverter modulation. In addition, different pulse width modulation patterns and the most suitable operating conditions for each braking mode have been studied. Finally, experimental results are presented to demonstrate the validity and effectiveness of the proposed braking torque control scheme.

Front-End Buck Rectifier With Reduced Filter Size and Single-Loop Control

This paper presents a transformerless solution for front-end rectification, which is particularly suitable for traction applications, requiring high voltages to be stepped down to appropriate dc voltage. The proposed topology is based on pulsewidth-modulation buck rectifier (current source inverter topology) and is capable of rectification and stepping down of single-phase ac supply, in a single stage. A new control scheme is proposed to achieve constant dc output voltage and sinusoidal source current, irrespective of large ripples in the dc inductor current. The proposed scheme is configured in single-loop voltage control mode. The relevant small-signal model is derived from the large-signal model using multiorder decomposition. An elaborate procedure of dc filter design is discussed, for circuit operation with minimum energy storage. All analytical results are validated by numerical simulation for sinusoidal and distorted source voltage. Experimental verification is achieved through a 1.2-kW grid-connected laboratory prototype.

Impact of Current Ripple on Li-ion Battery Ageing

The aim of this paper is to investigate the impact of the current ripple, originating from the dc-dc converter of e.g. a PHEV powertrain, on the ageing of Li-ion batteries. Most research concerning batteries focuses on very low (μHz) to low (Hz) frequencies and low current ripples to create very accurate battery models which can determine e.g. the State of Charge of the battery. On the other hand the design of dc-dc converters tries to reduce the current ripple by using multiple phases with interleaving technique and capacitors in parallel with the battery. The interaction between the current ripple of the dc-dc converter and the battery has received little attention so far. A test set-up is build with two identical 304 V , 12 kWh Li-ion batteries and two 100 A dc-dc converters. The dc-dc converter can be connected to an LCL-filter or solely to the primary inductor of this filter, such that the battery current contains a small or large current ripple respectively. The batteries are discharged and charged to simulate the circumstances in which a plug-in hybrid electric vehicle is used. After each month, during which the battery either experiences a small or large current ripple, characterization tests are performed to establisch the ageing of the batteries. Based on the test results, the current ripple does not appear to have a measurable impact on the battery resistance and the Discharge and Regen Power. There is an increase of the resistance and a decrease of the Discharge and Regen Power, but this is to be expected as the battery packs are submitted to 3 months of Combined Cycle Life Testing. The temperature of the battery turns out to be far more important for the resistance and attained power levels of the batteries. The absent effect of the current ripple on the ageing of the batteries may be due to the intrinsic double-layer capacitor. This capacitor at the surface of the electrodes carries part of the current ripple and reduces the current ripple as experienced by the actual charge transfer reaction which carries the dc-part of the current.

Temperature-Driven Reversible Rippling and Bonding of a Graphene Superlattice

In order to unravel the complex interplay between substrate interactions and film configuration, we investigate and characterize graphene on a support with non-three-fold symmetry, the square Ir(100). Below 500 °C, distinct physisorbed and chemisorbed graphene phases coexist on the surface, respectively characterized by flat and buckled morphology. They organize into alternating domains that extend on mesoscopic lengths, relieving the strain due to the different thermal expansion of film and substrate. The chemisorbed phase exhibits exceptionally large one-dimensional ripples with regular nanometer periodicity and can be reversibly transformed into physisorbed graphene in a temperature-controlled process that involves surprisingly few C-Ir bonds. The formation and rupture of these bonds, rather than ripples or strain, are found to profoundly alter the local electronic structure, changing graphene behavior from semimetal to metallic type. The exploitation of such subtle interfacial changes opens new possibilities for tuning the properties of this unique material.

A New FOC Approach of Induction Motor Drive Using DTC Strategy for the Minimization of CMV

This paper presents a New FOC Approach of Induction Motor Drive using DTC Strategy for the Minimization of CMV (common mode voltage) with the switching tables for the generation of PWM signals. High performance induction motor drives require a better transient and steady state performance. To achieve high performance, there are two control strategies namely, field oriented control (FOC) and direct torque control (DTC) for induction motor drives. Though these two methods give better transient performance, the FOC needs reference frame transformations and DTC gives large steady state ripples. To overcome these drawbacks, this paper presents a novel FOC algorithm for induction motor drives, which combines the principles of both FOC and DTC. The proposed method uses a predetermined switching table instead of a much more time consuming pulse width modulation (PWM) procedure. This approach gives a quick torque response like DTC and gives reduced ripple like FOC. The switching table is based on the conventional DTC principle, which gives good performance with reduced common mode voltage variations. To validate the proposed method numerical simulations have been carried out and compared with the existing algorithms. The simulation results confirm the effectiveness of the proposed method. DOI: http://dx.doi.org/10.11591/ijpeds.v3i2.2416

Vector Control Based on SVPWM for ACIM

To solve the large torque ripple and current harmonics, low DC bus voltage problems, a new control strategy is proposed for AC induction motor by using space vector pulse width modulation, so that the static and dynamic performance are improved. The system simulation experiment mode was established based on SVPWM to verify the effectiveness of the system control mode. It is showed that it can reduce the current ripple and torque ripple, improve the utilization of DC bus voltage. It means that the control strategy based SVPWM can improve dynamic and static performance effectively for the ACIM servo system.

DC‐bus voltage control of grid‐connected voltage source converter by using space vector modulated direct power control under unbalanced network conditions

Unbalanced grid voltage will cause large dc-bus voltage ripple and introduce high harmonic current components on the grid side. This will severely threaten the safety of the grid-connected voltage source converter (VSC) and consequently, affect the healthy operation condition of the load. In this study, a new proportional-integral-resonant (PI-RES) controller-based, space vector modulated direct power control topology is proposed to suppress the dc-bus voltage ripple and in the same time, controlling effectively the instantaneous power of the VSC. A special ac reactive power reference component is introduced in the controller, which is necessary in order to reduce the dc-bus voltage ripple and active power harmonics at the same time. The proposed control topology is implemented in the lab. Simulation and experimental results are provided to validate its performance and the analysis presented in this study.

Molecular dynamics study on the bending rigidity of graphene nanoribbons

The electromechanical responses of a graphene nanoribbon, such as its ripple magnitude, bending rigidity and effective spring constant, were investigated via classical molecular dynamics simulations and the elastic plate theory with a view to future engineering applications of graphene-nanoribbon-based nanoelectromechanical devices. While the bending rigidity was low for large ripples, it was high for very small ripples. However, on most ripple scales, the values of the bending rigidity remained constant around 2.3eV. The bending rigidity gradually increased from about 1.2 to 2.37eV with increasing deflection, after that, the bending rigidity slightly decreased to 2.29eV with further increases in deflection, and finally rapidly increased to 2.93eV with increasing deflection until the breaking point. The effective spring constant increased to 0.36N/m with increasing applied force and deflection, in the linear elastic region it remained below ∼0.25N/m.

Novel Design for Direct Torque Control System of PMSM

Nowadays, with the rapid development of high-performance servo system, The conventional permanent magnet synchronous motor (PMSM) Direct Torque Control (DTC) system has large torque ripple in low speed which cannot be well adapted to today`s development. The main reason is because the number of voltage vectors provided by the two-level inverter is only six and the relationship between voltage vector and torque is not clear[1-5.10-12]. In this paper, the basic concept of direct torque control of permanent magnet synchronous motor is investigated in order to emphasize the effects produced by a given voltage vector on stator and torque variations in this paper. Modified the voltage sector switching table, a novel DTC scheme for the permanent magnet synchronous motor is proposed which is using a novel three-level inverter. An improvement of the drive performance can be obtained by using the novel DTC scheme. The simulation results showed that the scheme could reduce the torque ripple in low speed and improved the stability of the motor under the condition of keeping the system dynamic performance. DOI: http://dx.doi.org/10.11591/telkomnika.v11i4.2391

Active current ripple cancellation in parallel connected buck converter modules

Parallel connection of converters has become a popular method of improving efficiency. This study first presents a design technique for a buck converter with two parallelly connected power modules (PMs), where one PM is designed with large current ripple for high efficiency. This study then demonstrates an active current ripple cancellation technique, where the current waveform of the second PM is shaped to be the exact opposite to that in the first PM, to reduce the current ripple as seen by the output capacitor. The factors that affect the overall efficiency in a parallel connected converter and the calculation of the parameters that determine the effectiveness of the ripple cancellation are reported. A prototype parallel converter is designed based on the proposed converter design technique and the current ripple seen by the output capacitor is successfully reduced by 66% with the proposed ripple cancellation technique, under different line and load conditions.

Active toroidal field ripple compensation and MHD feedback control coils in FAST

The Fusion Advanced Study Torus (FAST) has been proposed as a high magnetic field, compact size tokamak providing a flexible integrated environment to study physics and technology issues in ITER and DEMO relevant conditions.FAST has a quite large natural toroidal field ripple (around 1.5%) due to its compactness and to the number of access ports: this ripple must be lowered to an acceptable level to allow safe operations and a good confinement quality. An Active Ripple Compensating System (ARCS) has been designed, based on a set of poloidal coils placed between the plasma chamber and the Toroidal Field Coils (TFCs). These ARCS coils will be fed with adjustable currents, opposite in direction respect to the TFC currents, and will allow lowering the ripple up to zero and beyond.The CAD model of FAST including the ARCS coils has been completed and preliminary electromagnetic and thermal analyses have been carried out.Moreover, a Feedback Active Control System (FACS) composed of two arrays of in-vessel saddle coils has been designed to allow safe high plasma current, low safety factor operation and to mitigate possibly large ELMs effects in FAST. These FACS coils will be fed by a feedback system to control MHD modes: a first engineering assessment of the current requirements has been carried out.

Size Reduction in Low-Frequency Square-Wave Ballasts for High-Intensity Discharge Lamps Using Soft-Saturation Magnetic Material and Digital Control Techniques

This paper presents an approach to reduce the size of low-frequency square-wave (LFSW) ballasts by using a single stage for resonant ignition and LFSW operation together with soft-saturation magnetic material and digital control techniques. Inductor design constraints are developed to leverage the nonlinear inductor behavior and achieve both size reduction and desirable performance in lamp ignition, warm-up, and normal operation modes. The digital controller provides multiple functions, including 1) a phase-controlled resonant sweep to achieve reliable lamp ignition and device protection with zero-voltage switching despite the nonlinear tank inductance, 2) lamp ignition detection and rapid transition to LFSW mode for lamp warm-up, 3) fast LFSW polarity transitions with optimal timing control for acoustic resonance free operation, and 4) two-loop feedback control. A fast current control loop limits and stabilizes the lamp current and rejects large ripple from the power factor correction (PFC) stage in order to reduce the size of the PFC output capacitor. A slow power control loop rejects variations in the lamp characteristics during warm-up and lamp aging. Experimental results are presented showing successful ignition and operation of a 150-W high-intensity discharge lamp.

Torque ripple minimization and maximum power point tracking of a permanent magnet reluctance generator for wind energy conversion system

A permanent magnet reluctance generator (PMRG), which is the member of switched reluctance machine (SRM) family, has an extremely simple and robust structure: no winding on both rotor and stator. Required flux for energy conversion is provided by magnets buried in stator yokes. Thus, it seems to be suitable for wind energy conversion systems (WECSs) for reducing power generation cost to the level of fossil energy conversion systems. In a PMRG based conventional WECS, the PMRG is often accompanied by a simple diode bridge and a maximum power point tracking (MPPT) controlled converter. This type of converter topology does not allow utilizing any torque ripple minimization strategy. Thus, the system inevitably suffers from large torque ripples due to the doubly salient structure of both stator and rotor of the PMRG. Torque ripples propagate acoustic noise, vibrations, and mechanical stress in the turbine-shaft. Exposing to such ripples may result serious failure or damage in the WECS. In this paper, a novel algorithm consisting of MPPT and torque ripple control has been tested on the PMRG based WECS. The control strategy is applied to the system through an asymmetric half bridge (AHB) converter which is accepted to be a traditional converter for SRMs. The performance of control method has been verified under the conditions of constant and variable wind speed. Both simulation and experiment results prove that the control algorithm with the AHB converter allows significant torque ripple reduction in PMRG based WECS while generating power at its maximum point.

3상 PWM 정류기의 경부하시 입력전류 THD 저감을 위한 d축 전류리플 저감 PWM 방법

In this paper, a new PWM method is proposed to reduce the input current harmonics of 3 phase PWM rectifier. In the conventional carrier comparison PWM method, a triangular wave is generally used as the carrier wave. However, the large d-axis current ripple by the triangle carrier wave may be a source of large input current THD(Total Harmonic Distortion). In this paper, a new carrier comparison PWM method with saw tooth wave is proposed. Depending on the sector where the voltage command vector places, one of the rising or falling saw tooth wave is selected. To reduce the switching losses of the saw tooth carrier PWM, the discontinuous PWM is also presented. The proposed PWM method can reduce the d-axis current ripple as well as the switching losses. The performance of the conventional and proposed PWM methods is verified by the simulation and experimental results.

GENETIC BASED PLUS INTEGRAL CONTROLLER FOR PMBLDC MOTOR CONTROL USING RESONANT POLE INVERTER

Permanent Magnet Brushless DC (PMBLDC) motor drives are increasingly popular in industrial applications due to rapid progress of technologies in power electronics and the growing demand for energy saving. The increasing demand of energy saving from society is the external force for the development of PMBLDC motor drives. It is however driven by a hard-switching Pulse Width Modulation (PWM) inverter, which has low switching frequency, high switching loss, high Electro-Magnetic Interference (EMI), high acoustic noise and low efficiency, etc. To solve these problems of the hard-switching inverter, many soft-switching inverters have been designed in the past. Unfortunately, high device voltage stress, large dc link voltage ripples, complex control scheme and so on are noticed in the soft-switching inverters. This study introduces a novel genetic-proportional Plus Integral (PI) controller based resonant pole inverter using transformer, which can generate dc link voltage notches during chopping which minimize the drawbacks of soft-switching. Hence all switches work in zero-voltage switching condition. The performance of the genetic-based PI controller is compared with conventional PI controller. The experimental results show that the genetic-based PI controller renders a better transient response than the conventional PI controller resulting in negligible overshoot, smaller settling time and rise time. Moreover the proposed controller provides low torque ripples and high starting torque. Both simulation and experimental results are presented to show the superiority of the proposed GA-PI controller based resonant pole inverter.

A Flicker-Free Electrolytic Capacitor-Less AC–DC LED Driver

The electrolytic capacitor is the key component that limits the operating lifetime of LED drivers. If an ac–dc LED driver with power factor correction (PFC) control is allowed to output a pulsating current for driving the LEDs, the electrolytic capacitor will no longer be required. However, this pulsating current will introduce light flicker that varies at twice the power line frequency. In this paper, a configuration of flicker-free electrolytic capacitor-less single-phase ac–dc driver for LED lighting is proposed. The configuration comprises an electrolytic capacitor-less PFC converter and a bidirectional converter, which serves to absorb the ac component of the pulsating current of the PFC converter, leaving only a dc component to drive the LEDs. The output filter capacitor of the bidirectional converter is intentionally designed to have a large voltage ripple, thus its capacitance can be greatly reduced. Consequently, film capacitors can be used instead of electrolytic capacitors, leading to the realization of a flicker-free ac–dc LED driver that has a long lifetime. The proposed solution is generally applicable to all single-phase PFC converters. A prototype with 48-V, 0.7-A output is constructed and tested. Experimental results are presented to verify the effectiveness of the flick-free electrolytic capacitor-less ac–dc LED driver.